side the chests was no more than plus or minus 0.3C.
analyzed simply by extracting the analytes of interest
After an experiment each bag was opened and the mine
from the bags with acetonitrile after a suitable period
removed. From 5 to 20 mL of acetonitrile (HPLC Grade,
of exposure.
Burdick and Jackson) was added and the bag reclosed
with the crimp seals. The solvent was allowed to con-
Sorption of ERC on Tedlar
tact all the surfaces briefly, decanted into a vial, and 1
A section about 10 cm square was cut from a stan-
mL was removed for analysis.
dard Tedlar bag, 2 mils (0.005 cm) in thickness. It was
exposed to saturated TNT vapor at 22C in a glass desic-
For water collection, mines were submerged indi-
cator jar for 24 hours. The specimen was removed and
vidually in an appropriate volume of MilliQ water in a
immediately extracted by immersion in acetonitrile for
silanized glass jar. The setup was agitated gently on a
platform shaker in a dark room controlled at 21.5C.
a few minutes. The amount of TNT recovered was about
4 g, which corresponds to roughly a monolayer on
We took 3-mL water samples periodically for analysis.
each side of the Tedlar film.
These experiments were continued until the flux reached
an apparently constant value (steady-state).
Water and acetonitrile extracts were analyzed by
Potential breakthrough of ERC in Tedlar
A double-bagging experiment was conducted in
HPLC-UV. Standard Analytical Reference Materials
which a PPM2 antipersonnel land mine was placed in a
(SARMS) for 1,3-dinitrobenzene (DNB), 2,4-
Tedlar bag as described above. The bagged mine was then
dinitrotoluene (DNT), 2,4,6-trinitrotoluene (TNT), and
placed in a second, slightly larger Tedlar bag and it was
hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) were
also sealed. The experiment was placed in a temperature-
obtained from the U.S. Army Environmental Center,
controlled room at 21.5C in the dark for 3 days. At the
Edgewood, Maryland. A working stock containing 1.0
end of the experiment, the mine was removed and both
mg/L of each analyte in acetonitrile was prepared. Water
bags rinsed with acetonitrile and the extracts analyzed.
samples were diluted with one part acetonitrile, and
The outer bag contained no detectable ERC residues
acetonitrile extracts and stock standards were diluted
(less than 10 ng), while the inner bag contained 24,000
with three parts MilliQ water. All samples and stan-
dards were filtered through 0.45-m Durapore (Waters)
ng of DNT plus lesser amounts of the other ERC
membrane syringe (B-D) filters prior to analysis. A 10-
residues. After 7 days the inner bag contained about
cm column containing LC-8 was used to separate the
52,000 ng of DNT, while the outer bag had about 20
analytes using water:isopropanol (17:3) as the mobile
ng. Other ERC residues also showed less than 1% break-
phase at a flow rate of 1.4 mL/min.
through. This test assured us that losses attributable to
permeation of the Tedlar film by ERC were not signifi-
cant in these experiments (all the experiments reported
PRELIMINARY EXPERIMENTS
on here were completed in less than 1 week). Lower
temperatures would be expected to retard permeation
Unsuitability of Tedlar bag/solid phase
even more.
microextraction/headspace analysis
for determination of fluxes
Initially, ERC vapors were to be collected in Tedlar
RESULTS AND DISCUSSION
plastic bags, as this is a standard method of collecting
environmental gas samples for analysis. We assumed
Fluxes in air
The experimental fluxes determined by the Tedlar
that this method would also be reliable for collecting
bag method are compiled in Appendix A. They show
semi-volatile compounds, such as the ERC of interest.
the variability among mines within each type and among
Subsequently, several Tedlar bags were prepared, each
the different types. As one might expect, the inter-type
containing a land mine, and closed with an air-tight seal.
variability is much greater than the intra-type variabil-
A septum port allowed for solid phase microextraction
ity. Within types the relative standard deviations for each
(SPME) sampling of the bag headspaces and analysis
analyte were mostly less than 50%.
by a non-equilibrium method developed by Jenkins et
The mean flux values for each of the major analytes
al. (1999). Monitoring vapor concentrations with time
in this fashion gave erratic results. Compared with the
for each mine type were analyzed as a function of tem-
amount recovered by acetonitrile extraction of bag sur-
perature. Because chemical fluxes are seen to be anal-
faces, the amounts in the headspace were insignificant.
ogous to other chemical rate processes, an exponential
Although this precluded the conventional use of Tedlar
model of the form
bags to collect ERC vapors for analysis, these experi-
F = aebt
ments suggested that the bag surfaces themselves could
be used to capture TNT vapors, which could then be
was a logical choice, where F denotes flux, t is temper-
2
Previous Page
